My PC Suddenly Stopped Booting During a Gaming Session – Any Ideas?

Last night, during a long gaming session, my PC just stopped displaying on my monitors, even though the lights and fans were still running. I tried resetting the CMOS and reseating the RAM, but it didn't help. This morning, I swapped out RAM sticks and reset the CMOS again, yet it still won't boot. The red debug LED on my motherboard indicates there's a CPU problem. I'm planning to grab some isopropyl alcohol to clean and reapply the thermal paste after reseating the CPU. If that doesn't work, what should I do? It's strange for a system that worked flawlessly for several weeks to just fail like this. Specs include a 9800x3d CPU, RTX 5080 GPU, and 32 GB of G.Skill 6000MHz RAM. Update: After applying new thermal paste, there's still a red CPU LED on the motherboard. I'm really at a loss here.